A rock cutting head is known from DE 33 16 840 A1. This document describes a rock cutting head with a housing mountable to an extension arm or lug connection, wherein it is known herefrom to arrange a drive pinion in the rear portion of the housing directly or indirectly connected to the rotational drive. The housing is closed or terminated by a plate in the rear portion. Intermediate wheels are provided as a gear connection between the drive pinion and a spur-toothed wheel. It further follows from this document that in the front portion of the housing the shafts of the two cutting drums connected to the spur-toothed wheel are arranged in outer bearing hubs in the front portion of the housing. This construction is relatively cumbersome and prone to wear.
From DE 38 20 264 A1 it is known to form the housing of a drive assembly for the cutting or hewing heads or drums of a shearing and heading machine from steel in one piece.
Rock cutters are furthermore known from tunnel construction and mining, where they are used as advance working or mining machines accomodated to the respective conditions, usually provided with only one rotating cutting head. Cutting heads with two cutting drums are also known, which are used for heavy universal diggers in alternative use together with digging tools.
In the construction of cutting heads problems arise in that for effective advance work the cutting drum shall be able to cut into solid rock of the facing in an unimpeded manner without being impaired by its connection to the extension arm of the advance working machine and without endangering this connection. In order to keep low the constructional requirements for long load transmission paths and their encapsulation, it is also necessary to arrange the drive motor and a corresponding step-down gear as close to the cutting drum as possible, at the same time, however, protecting these drive means against external influences by the rough working operation.
In order to achieve this it is known to house a step-down planetary gear directly in the cutting drum, or, with a cutting head with two uni-axial cutting drums, to re-orientate the actuation thereof from a hydro- or electric motor arranged centrally in the connection housing by means of bevel wheels. In view of the fact that cutting drums are stressed up to the point of standstill during usage, and are often abusively used as digging-or handling tools, thereby caused overloads necessarily lead to premature gear defects. As especially with planetary gears all toothed wheels engage one another in close arrangement, the splintering off of a small part of a bearing or a tooth is sufficient to destroy the whole gear to an extent that repair work can usually not be undertaken in an economically viable manner. Furthermore, the danger exists that by introducing forces, which a digging tool exchangeably mounted on an extension arm can withstand, the substantially more sensitive cutting head will be overstressed and its housing at least elastically deformed, whereby the bevel wheel gear can be destroyed.